Flat panel display with improved white balance

ABSTRACT

Disclosed is a flat panel display capable of improving a white balance by making channel regions of transistors of R, G and B unit pixels with different current mobilities. The flat panel display includes a plurality of pixels, each of the pixels including R, G and B unit pixels to embody red (R), green (G) and blue (B) colors, respectively, and each of the unit pixels including at least one transistor. Channel layers of the transistors of at least two unit pixels among the R, G and B unit pixels have different current mobilities from one another. The R, G, B unit pixels includes transistors and the transistor of at least one unit pixel among the R, G and B unit pixels includes the channel layer made of silicon layers of different film qualities.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of Korean Patent ApplicationNo. 2003-24503 and 2003-24429, filed Apr. 17, 2003, the disclosure ofwhich is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The present invention is related to a full color flat paneldisplay and, more particularly, to a flat panel display and a method formanufacturing the same, capable of embodying a white balance by making achannel layer of a driving transistor in each of R, G and B unit pixelshave different current mobilities using MIC/MILC processes.

BACKGROUND OF THE INVENTION

[0003] Generally, as shown in FIG. 1, an organic light emitting diode(OLED) of a flat panel display includes a plurality of pixels 100 whichare arranged in the form of matrix. Each pixel 100 consists of threeunit pixels, that is, a unit pixel 110R for embodying a red (R), a unitpixel 120G for embodying a green (G) and a unit pixel 130B for embodyinga blue (B).

[0004] The R unit pixel 110R includes a red electroluminescence (EL)device 115 including a red (R) light emitting layer, a drivingtransistor 113 for supplying a current to the red EL device 115, and aswitching transistor 111 for switching the current supply from thedriving transistor 113 to the red EL device 115.

[0005] The G unit pixel 120G includes a green EL device 125 including agreen (G) light emitting layer, a driving transistor 123 for supplying acurrent to the green EL device 125, and a switching transistor 121 forswitching the current supply from the driving transistor 123 to thegreen EL device 125.

[0006] The B unit pixel 130B include a blue EL device 135 including ablue (B) light emitting layer, a driving transistor 133 for supplying acurrent to the blue EL device 135, and a switching transistor 131 forswitching the current supply from the driving transistor 133 to the blueEL device 135.

[0007] Conventionally, the driving transistors 113, 123 and 133 of theR, G and B unit pixels 110R, 120G and 130B of an OLEDhave the same size,that is, the same ratio W/L of the width W to the length L of thechannel layer, and the order of the EL devices in the order of theirluminous efficiency is B, R and G unit pixels. In the conventional OLED,since the sizes of the channel layers of the driving transistors 113,123 and 133 in the R, G, and B unit pixels 110R, 120G and 130B are samewhile the luminous efficiencies of R, G and B EL devices 115, 125 and135 are different from one another, it was difficult to embody the whitebalance.

[0008] In order to embody the white balance, a relatively small quantityof current should be supplied to the EL device having high luminousefficiency, for example, the green EL device, and a relatively largequantity of current should be supplied to the red and blue EL deviceshaving lower luminous efficiencies.

[0009] Here, since a current Id flowing to the El device through thedriving transistor begins to flow when the driving transistor is in thesaturation state, the current is expressed as follows.

Id=CoxμW(Vg−Vth)²/2L  (1)

[0010] Therefore, one of the methods for controlling the current flowingto the EL device in order to embody the white balance is to make thesize of the driving transistors of the R, G and B unit pixels, that is,the ratio W/L of the width W to the length L of the channel layerdifferent and then to control the quantity of the current flowing to theEL devices of the R, G and B unit pixels. The method for controlling thequantity of current flowing to the EL device in accordance with the sizeof the transistor is disclosed in the Japanese Laid-open PatentPublication No. 2001-109399. In this Japanese patent, sizes of thedriving transistors of the R, G and B unit pixels are formed differentlyin accordance with the luminous efficiencies of the EL device in each ofthe R, G and B unit pixels. That is, the quantity of the current flowingto the EL device of the R, G and B unit pixels is controlled by makingthe size of the driving transistor of the unit pixel to embody the green(G) having a higher luminous efficiency smaller than that of the drivingtransistor of the unit pixel to embody the red (R) or blue (B) having arelatively lower luminous efficiency.

[0011] Another method to embody the white balance is to make thedimensions of the light emitting layers of R, G and B unit pixelsdifferent, which is disclosed in the Japanese Laid-open PatentPublication No. 2001-290441. In the Japanese patent, same luminance isgenerated from the R, G and B unit pixels by making the light emittingareas different in accordance with luminous efficiencies of the ELdevices of the R, G and B unit pixels. That is, same luminance isgenerated from the R, G and B unit pixels by making light emitting areasof the R or B unit pixel having low luminous efficiencies larger thanthe G unit pixel having high luminous efficiency, relatively.

[0012] However, in the conventional method for embodying the whitebalance described above, the light emitting area of the unit pixelhaving low luminous efficiency among the R, G and B unit pixels is madelarger, or increasing the size of the transistor of the unit pixelhaving low luminous efficiency among the R, G and B unit pixels. Thereoccurs a problem that the area charged in each pixel is increased, andtherefore it is not easy to apply the method to a high definitiondisplay.

SUMMARY OF THE INVENTION

[0013] It is an aspect of the present invention to provide a flat paneldisplay and a method for manufacturing the same wherein a white balancemay be embodied without increasing the area of a pixel.

[0014] Another aspect of the present invention provides a flat paneldisplay and a method for manufacturing the same wherein a white balancemay be embodied by making channel layers of a driving transistors in R,G and B unit pixel have different current mobilities.

[0015] It is yet a further aspect of the present invention to provide aflat panel display and a method for manufacturing the same wherein awhite balance may be embodied by making channel layers of drivingtransistors in R, G and B unit pixels have different directions ofcrystallization.

[0016] Yet another aspect of the present invention provides a flat paneldisplay and a method for manufacturing the same wherein a white balancemay be embodied by making resistance values of channel layers of drivingtransistors in R, G and B unit pixels different.

[0017] Yet another aspect of the present invention provides a flat paneldisplay and a method for manufacturing the same wherein a white balancemay be embodied by making a length of an amorphous silicon film includedin the channel layer of the driving transistor in each R, G and B unitpixel different.

[0018] According to an exemplary embodiment of the present invention,there is provided a flat panel display comprising a plurality of pixels,where each of the pixels includes R, G and B unit pixels to embody red(R), green (G) and blue (B) colors, respectively, and where each of theunit pixels includes at least one transistor, wherein transistors of atleast two unit pixels of the R, G, and B unit pixels include channellayers of different current mobilities.

[0019] The at least one transistor of the R, G and B unit pixelsincludes a channel layer having the same size in each pixel. The R, Gand B unit pixels include light-emitting devices, respectively.Transistors to control currents supplied to the light emitting devicesof each unit pixel include channel layers having the same size in eachpixel, and current mobility of a transistor to drive a light-emittingdevice having the highest luminous efficiency among the lightingemitting devices of the unit pixels is lower than the current mobilityof a transistor to drive light-emitting devices having a relativelylower luminous efficiency.

[0020] The channel layers of the transistors of the R, G and B unitpixels may be made of polycrystalline silicon films having differentcrystallization directions from one another. A channel layer of atransistor to drive a light-emitting device having the highest luminousefficiency among the light-emitting devices may be made of a metalinduced crystallization (MIC) polycrystalline silicon film, and channellayers of transistors to drive light-emitting devices having arelatively low luminous efficiency may be made of a metal inductedlateral crystallization (MILC) polycrystalline silicon film.

[0021] The R, G and B unit pixels may further include light-emittingdevices driven by the transistors respectively, and the R, G and B unitpixels each include a driving transistor to drive the light-emittingdevice and a switching transistor to switch the driving transistor on oroff.

[0022] The channel layers of the switching transistors of the R, G and Bunit pixels may be made of a MIC polycrystalline silicon film. A drivingtransistor of a unit pixel having the highest luminous efficiency amongthe R, G and B unit pixels has a channel layer made of the MICpolycrystalline silicon film, and the driving transistors of unit pixelshaving a relatively low luminous efficiency have channel layers made ofa MILC polycrystalline silicon film.

[0023] The channel layers of the switching transistors of the R, G and Bunit pixels may be made of a MILC polycrystalline silicon film, and adriving transistor having the highest luminous efficiency among the R, Gand B unit pixels may be a channel layer made of a MIC polycrystallinesilicon film, while driving transistors of unit pixels having relativelylow luminous efficiency may have channel layers made of a MILCpolycrystalline silicon film.

[0024] A switching transistor and a driving transistor of a unit pixelhaving the highest luminous efficiency among the R, G and B unit pixelsmay have channel layers made of a MIC polycrystalline silicon film, anddriving transistors and switching transistors of unit pixels having arelatively low luminous efficiency may have channel layers made of aMILC polycrystalline silicon film.

[0025] Also, in a flat panel display which comprises a plurality ofpixels, each of the pixels including R, G and B unit pixels, and each ofthe unit pixels including at least one transistor, there is provided amethod for manufacturing the flat panel display, comprising forming anamorphous silicon film on an insulating substrate and forming a firstand a second MILC masks on the amorphous silicon film. The methodfurther comprises depositing a metal film for MILC over the substrate,crystallizing the amorphous silicon film into a polycrystalline siliconfilm in order that a portion corresponding to the first and second masksis crystallized by a MILC method and a remaining portion is crystallizedby a MIC method, removing the first and second masks and the metal film,and patterning the polycrystalline silicon film in order that asemiconductor layer of a transistor of a unit pixel having the highestluminous efficiency among the R, G and B unit pixels is made of thepolycrystalline silicon film crystallized by the MIC method, andsemiconductor layers of transistors of unit pixels having the relativelylow luminous efficiency is made of the polycrystalline silicon filmcrystallized by the MILC method.

[0026] Also, there is provided a flat panel display, comprising aplurality of pixels, each of the pixels including R, G and B unit pixelsto embody red (R), green (G) and blue (B) colors, respectively, each ofthe unit pixels including a transistor, wherein the transistor of atleast one unit pixel among the R, G and B unit pixels includes a channelregion made of silicon layers having different film quality.

[0027] The transistors of the at least two unit pixels among the R, Gand B unit pixels include channel regions made of silicon layers of atleast one different film quality, and lengths of the silicon layershaving a low current mobility are different in the channel regions.

[0028] The R, G and B unit pixels include light-emitting devices,respectively, and a channel region of a transistor corresponding to alight-emitting device having the lowest luminous efficiency among thelight-emitting devices of the R, G and B unit pixels does not includethe silicon layer having a low current mobility or includes the siliconlayer having low current mobility which has a smaller length thanchannel regions of transistors corresponding to light-emitting deviceshaving relatively luminous efficiency.

[0029] The channel region is made of a polycrystalline silicon layer andan amorphous silicon layer and the silicon layer having the low currentmobility in the channel region is made of the amorphous silicon layer.

[0030] Also, in a flat panel display which comprises a plurality ofpixels, each of the pixels including R, G and B unit pixels to embodyred (R), green (G) and blue (B) colors, respectively, each of the unitpixels including a transistor, unit pixels, and each unit pixelcomprises a transistor, there is provided a method for manufacturing theflat panel display, comprising forming an amorphous silicon film on aninsulating substrate forming a first to a third masks for MILC on theamorphous silicon film and depositing a metal film for MILC over thesubstrate. The method further comprises crystallizing the amorphoussilicon film into a polycrystalline silicon film in order that theamorphous silicon film only partially remains under the first to thirdmasks removing the first to third masks for MILC and the metal film forMILC, and patterning the polycrystalline silicon film in order that theamorphous silicon film existing between the polycrystalline siliconfilms forms semiconductor layers on the transistors of the R, G and Bunit pixels, wherein channel regions of the transistors of the R, G andB unit pixels have resistance values determined by the length of theamorphous silicon film existing between the polycrystalline siliconfilms.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and other features and advantages of the presentinvention will become more apparent to those of ordinary skill in theart by describing in detail embodiments thereof with reference to theattached drawings.

[0032]FIG. 1 is a view showing an arrangement of R, G and B unit pixelsof a conventional flat panel display.

[0033]FIGS. 2A, 2B, 2C and 2D are views showing a method formanufacturing driving transistors of R, G and B unit pixels inaccordance with an embodiment of the present invention.

[0034]FIG. 3 is a view showing a relationship between a gate voltage anda drain voltage in accordance with MIC/MILC crystallization methods.

[0035]FIGS. 4A, 4B, 4C and 4D are sectional views of a method formanufacturing driving transistors of R, G and B unit pixels inaccordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention will now be described more fullyhereinafter with reference to the accompanying drawings, in whichembodiments of the invention are shown. This invention may, however, beembodied in different forms and should not be construed as limited tothe embodiments set fourth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art. Inthe drawings, the thickness of layers and regions may be exaggerated forclarity. Like numbers refer to like elements throughout thespecification.

[0037]FIGS. 2A, 2B, 2C, and 2D are views showing a method formanufacturing driving transistors of R, G and B unit pixels inaccordance with an embodiment of the present invention. Sectionalstructures of FIGS. 2A, 2B, 2C and 2D illustrate the driving transistorsamong the R, G and B unit pixels of each pixel in an organic lightemitting diode.

[0038] Referring to FIG. 2A, a buffer layer which is not shown in thedrawing, is formed on an insulating substrate 200, and an amorphoussilicon film 210 is formed on the buffer layer. A number of masks 221and 225 for MILC are formed on the amorphous silicon film 210, and ametal film 230 is formed on the entire surface of the substrate.

[0039] The masks 221 and 225 for MILC are formed on regions 201 and 205where the R and B unit pixels are to be formed correspondingly. Since amask for the MILC is not formed on a region 203 where G unit pixel is tobe formed, the metal film 230 is formed to contact with the amorphoussilicon film 210 directly. Although oxide films are used as the masks221 and 225 for MILC in the present invention, other films such as aphotosensitive film may be used instead of the oxide film.

[0040] Referring to FIG. 2B, the amorphous silicon film 210 iscrystallized as a polycrystalline silicon film 240 by performing acrystallization process. Here, the polycrystalline silicon film 240 iscrystallized by the MIC and MILC methods, wherein a portion 241 of thepolycrystalline silicon film 240 corresponding to the mask 221 iscrystallized by the MILC method, and a portion 245 corresponding to themask 225 is also crystallized by the MILC method. A portion 243 directlyin contact with the metal film 230, that is, the remaining portion 243including the region 203 where the G unit pixel is to be formed, isentirely crystallized by the MIC method.

[0041] Referring to FIG. 2C, after the masks 221 and 225 for MILC andthe metal layer 230 are removed, semiconductor layers 251, 253 and 255of the driving transistors of the R, G and B unit pixels are formed bypatterning the poly silicon film 240 using a mask (not shown in thedrawing) for forming the semiconductor layers of the drivingtransistors. Here, the semiconductor layers 251, 253 and 255 of thedriving transistors of the unit pixels are all of the same size.

[0042] The semiconductor layer 251 of the driving transistor of the Runit pixel among the R, G and B unit pixels is formed of the polysilicon film 241 crystallized by the MILC method. The semiconductorlayer 253 of the driving transistor of the G unit pixel is formed of thepoly silicon film 243 crystallized by the MIC method The semiconductorlayer 255 of the driving transistor of the B unit pixel is formed of thepoly silicon film 245 crystallized by the MILC method.

[0043] Referring to FIG. 2D, a gate insulating film 260 is formed on thesubstrate including the semiconductor layers 251, 253 and 255, and gates271, 273 and 275 of the driving transistor of each unit pixel are formedon the gate insulating film 260. Source/drain regions 281, 283 and 285of each driving transistor are formed by performing ion implantation ofimpurities of a desired conductivity type into the semiconductor layers251, 253 and 255 using the gates 271, 273 and 275 as masks,respectively.

[0044] Even though it was not shown in the drawing, an interlayerinsulating film may be formed on the entire surface of the substrate.Contact holes for exposing the source/drain regions 281, 283 and 285 maybe formed by etching the interlayer insulating film and the gateinsulating film 260, and source/drain regions electrically connected tothe source/drain regions 281, 283 and 285 through the contact holes maybe formed, thereby manufacturing the driving transistor.

[0045] In a flat panel display of the present invention manufacturedusing the method described above, the driving transistors of the R, Gand B unit pixels may include channel layers having the same length Lrc,Lgc and Lbc. The driving transistors of the R and B unit pixels mayinclude the channel layers made of the poly silicon films 241 and 245crystallized by the MILC method, respectively, and the drivingtransistor of the G unit pixel may include the channel layer made of thepoly silicon film 243 crystallized by the MIC method. Therefore, thedriving transistors of the R, G and B unit pixels may have channellayers of the same size. Further, current mobilities of the channellayers may be changed in accordance with the crystallization directionsof the channel layers of the driving transistors of the R, G and B unitpixels.

[0046] The channel layers of the driving transistors of the R and B unitpixels which have relatively low luminous efficiencies may be made ofthe poly silicon films 241 and 245 crystallized by the MILC methodhaving high current mobility, and the channel layer of the drivingtransistor of the G unit pixel having a relatively high luminousefficiency may be made of the poly silicon film 243 crystallized by theMIC method having low current mobility.

[0047] Therefore, according to an embodiment of the invention, while aresistance value of the channel layer may be determined by changing thecrystallization direction of the channel layer in accordance with theluminous efficiencies of the EL devices of the R, G and B unit pixels,the channel layers of the driving transistors of the R and B unit pixelshaving very low luminous efficiencies relatively are made of polysilicon films crystallized by the MILC method having a crystallizationdirection of the same direction with the channel length, that is,horizontal direction, and accordingly have relatively low resistancevalues. Also, the channel layer of the driving transistor of the G unitpixel having a relatively high luminous efficiency is made of the polysilicon film crystallized by the MIC method having a crystallizationdirection of a perpendicular direction to the channel length, that is,vertical direction and accordingly has relatively high resistance value.

[0048] Accordingly, the white balance of the present invention may beembodied by making sizes of the channel layers of the R, G and B unitpixels the same and making the crystallization directions of themdifferent, and then making the current mobilities have different valuesfrom one another.

[0049]FIG. 3 is a view showing a relationship between a gate voltage anda drain voltage of thin film transistors including semiconductors layerscrystallized by the MIC and MILC methods. FIG. 3 shows that even in thecase of thin film transistors having the same sizes (W/L) and channeldirections, current quantities can be different in accordance with thefine structure of the poly silicon film of the channel layer.

[0050] Referring to FIG. 3, it is noted that the drain currentcharacteristic to the gate voltage of the MILC polycrystalline siliconthin film transistor is superior to that of the drain currentcharacteristics to the gate voltage of the MIC poly silicon thin filmtransistor. Therefore, the current mobility of the thin film transistormade of the poly silicon film crystallized by the MILC method is higherthan that of the thin film transistor made of the poly silicon filmcrystallized by the MIC method.

[0051] Accordingly, in one embodiment of the present invention, thechannel layer of the driving transistor of the green unit pixel having arelatively high luminous efficiency is made of the MIC polycrystallinesilicon film, and the channel layers of the driving transistors of thered and blue unit pixels having relatively low luminous efficiencies aremade of the MILC polycrystalline silicon films. The white balance may beembodied by increasing the current flowing through the drivingtransistor of the red or blue unit pixel more than current flowingthrough the driving transistor of the green unit pixel.

[0052] In one embodiment of the present invention, even though thechannel layers of the driving transistors are formed of polycrystallinesilicon films crystallized by the MIC and/or MILC method in accordancewith the luminous efficiencies of the R, G and B EL devices, this MICand/or MILC method may be applied to the switching transistors of the R,G and B unit pixels. For example, all of channel layers of the switchingtransistors of the R, G and B unit pixels may be formed of the polysilicon film crystallized by the MILC and/or the MIC method.Alternatively, the switching transistor of the G unit pixel having highluminous efficiency may have the channel layer formed of the polysilicon film crystallized by the MIC method and the switching transistorof the R or B unit pixel having low luminous efficiency may have thechannel layer formed of the poly silicon film crystallized by the MILCmethod. The semiconductor layers of the driving transistor and theswitching transistors of the R, G and B unit pixels may have the same ordifferent crystallization directions from the corresponding channellayer.

[0053] Even though the channel layer of one embodiment of the presentinvention is described as crystallized by the MIC/MILC, channel layersof the driving transistors of the R, G and B unit pixels may havedifferent crystallization methods from one another so that allcrystallization methods having different current mobilities from oneanother may be applicable to the present invention.

[0054]FIGS. 4A, 4B, 4C and 4D are sectional views of process showing amethod for manufacturing driving transistors of R, G and B unit pixelsin accordance with another embodiment of the present invention.Sectional structures of FIGS. 4A, 4B, 4C and 4D illustrate to thedriving transistors of the R, G and B unit pixels of each pixel in theorganic light emitting diode.

[0055] Referring to FIG. 4A, even though it was not shown in thedrawing, a buffer layer is formed on an insulating substrate 400 and anamorphous silicon layer 410 is formed on the substrate. A number ofmasks 421, 423 and 425 for MILC are formed on the amorphous siliconlayer 410 and a metal layer 430 is formed on the entire surface of thesubstrate.

[0056] The masks 421, 423 and 425 for MILC are formed with differentwidths from one another, wherein the order of the mask width from thetop is a second mask 423, a first mask 421 and a third mask 425. Thefirst mask 421 is formed on a region where the driving transistor (113in FIG. 1) of an R unit pixel among the R, G and B unit pixels is to beformed correspondingly, the second mask 423 is formed on a region wherethe driving transistor (123 in FIG. 1) of a G unit pixel is to beformed. The third mask 425 is formed on a region where the drivingtransistor (133 in FIG. 1) of a B unit pixel is to be formed.

[0057] Referring to FIG. 4B, a crystallization process to crystallizethe amorphous silicon film 410 to a polycrystalline silicon film 440 isperformed, wherein portions corresponding to the masks 421, 423 and 425among the amorphous silicon film 410 are crystallized intopolycrystalline silicon films 441, 443 and 445 by the MILC method. Aportion directly contacted with the metal layer 430 between the masks421, 423 and 425 is crystallized into a polycrystalline silicon film 447by the MIC method.

[0058] Since the first to third masks 421, 423 and 425 for MILC havedifferent widths from one another, a portion of the poly silicon film440 corresponding to the third mask 425 having a relatively low width iscrystallized by the MILC method and portions corresponding to the firstand second masks 421 and 423 having a relatively high widths arepartially crystallized by the MILC leaving the amorphous silicon films411 and 413 intact, respectively.

[0059] That is, the amorphous silicon film 411 exists between portions441 crystallized by the MILC method among the polycrystalline siliconfilm 440 corresponding to the first mask 421. Further, the amorphoussilicon film 413 exists between the portions 443 crystallized by theMILC method among the polycrystalline silicon film 440 corresponding tothe second mask. Since the width of the first mask 421 is relativelysmaller than the width of the second mask 423, the length of theamorphous silicon film 413 corresponding to the second mask 423 islarger than the length of the amorphous silicon film 411 correspondingto the first mask 421.

[0060] Referring to FIG. 4C, after removing the masks 421, 423 and 425used for the MILC method and the metal layer 430, semiconductor layers451, 453 and 455 for the driving transistors of the R, G and B unitpixels are formed by patterning the polycrystalline silicon film 440using a mask (not shown in the drawing) for forming the semiconductorlayer. The semiconductor layer 451 for the driving transistor of the Runit pixel among the R, G and B unit pixels is formed of the portions441 crystallized by the MILC method among the polycrystalline siliconfilms 440 and the amorphous silicon film 411 existing between theportions 441. The semiconductor layer 453 for the driving transistor ofthe G unit pixel is formed of the portions 443 crystallized by the MILCmethod among the polycrystalline silicon films 440 and the amorphoussilicon film 413 existing between the portions 443. On the other hand,the semiconductor layer 455 for the driving transistor of the B unitpixel is formed of the polycrystalline silicon film 445 onlycrystallized by the MILC method among the polycrystalline silicon films.

[0061] Referring to FIG. 4D, a gate insulating film 460 is deposited onthe entire surface of the substrate, including the semiconductor layers451, 453 and 455. A conductive material, such as a metal film, isdeposited on the film 460 and then gates 471, 473 and 475 of the drivingtransistors of each of the R, G and B unit pixels are formed bypatterning the conductivity material using a mask (not shown in thedrawing) for forming the gate. Then, source/drain regions 481, 483 and485 of the driving transistors are formed by performing an ionimplantation into the semiconductor layers 451, 453 and 455 with highconcentration impurities of desired conductive type using the gates 471,473 and 475 as masks.

[0062] Even though it was not shown in the drawing, the drivingtransistor may be manufactured by forming an interlayer insulating filmon the entire surface of the substrate, forming contact holes forexposing the source/drain regions 481, 483 and 485 by etching theinterlayer insulating film and the gate insulating film 460, and formingsource/drain electrodes electrically connected to the source/drainregions 481, 483 and 485 through the contact holes.

[0063] In a flat panel display in accordance with the present inventionmanufactured by the method described above, a channel layer 482 of thedriving transistor of the R unit pixel may be made of thepolycrystalline silicon film 441 crystallized by the MILC method and theamorphous silicon film 411. The length Lrc of the channel layer becomesthe sum of lengths Lr1 and Lr2 of the polycrystalline silicon film 441and the length Lra of the amorphous silicon film 411, that is,Lrc=Lr1+Lra+Lr2. A channel layer 484 of the driving transistor of the Gunit pixel is made of the polycrystalline silicon film 443 crystallizedby the MILC method and the amorphous silicon film 413. The length Lgc ofthe channel layer becomes the sum of lengths Lg1 and Lg2 of thepolycrystalline silicon film 443 and the length Lga of the amorphoussilicon film 413, that is, Lgc=Lg1+Lga+Lg2. A channel layer 486 of thedriving transistor of the B unit pixel is made of the polycrystallinesilicon film 445 only crystallized by the MILC method, and the lengthLbc of the channel layer is identical with the length Lb of thepolycrystalline silicon film 445.

[0064] In the driving transistors of each of the R, G and B unit pixels,since the lengths of the channel layers 482, 484 and 486 are same asLrc=Lgc=Lbc, the resistance values of the channel layers of the drivingtransistors are changed in accordance with lengths of the amorphoussilicon films included in each channel layer. While embodiments of thepresent invention may be constructed to determine the resistance valuesof the channel layers in accordance with the luminous efficiencies ofthe EL devices of the R, G and B unit pixels, since the channel layer486 of the B unit pixel having the lowest luminous efficiency relativelyis made of the polycrystalline silicon film crystallized by the MILCmethod, the resistance value of the channel layer is relatively low.

[0065] Also, the channel layer 282 or 284 of the R or G unit pixelhaving a relatively high luminous efficiency includes an amorphoussilicon film between the polycrystalline silicon films so that theresistance value of the channel layer is increased relatively. Since theEL device of the R unit pixel has a luminous efficiency lower than thatof the EL device of the G unit pixel, the length Lra of the amorphoussilicon film 411 existing in the channel layer 482 of the R unit pixelis formed to be shorter than the length Lga of the amorphous siliconfilm 413 existing in the channel layer 484 of the G unit pixel,relatively.

[0066] Accordingly, while the lengths of the channel layers of thedriving transistors of the R, G and B unit pixels in accordance withanother embodiment of the present invention are formed to be same, theamorphous silicon films existing in the channel layers of the drivingtransistors of the R, G and B unit pixels are formed to have differentlengths from one another. Therefore, the white balance can be embodiedby making the resistance values of the channel layers of the drivingtransistors different from one another.

[0067] In accordance with another embodiment of the present invention,the resistance values of the channel layers of the driving transistorsof the R, G and B unit pixels are changed by performing thecrystallization process in order that the amorphous silicon film existsamong the channel layers through the MILC process. However, methods forchanging resistance values of the driving transistors of the R, G and Bunit pixels may be applicable to the present invention by making thechannel layer include the amorphous silicon films having differentlengths from one another using other crystallization process instead ofthe MILC process. Even though there may be no amorphous silicon film inthe channel layer of the driving transistor of the B unit pixel, thepresent invention is not restricted to the construction described above.Rather, the present invention can be formed even with a constructionincluding an amorphous silicon film having a resistance value in a levelcapable of embodying the white balance to the channel layer of the R orG unit pixel.

[0068] In accordance with another embodiment of the present invention, acrystallization process can be performed so that an amorphous siliconfilm exists in each channel layer by controlling a crystallizationtemperature or a crystallization time when performing MILCcrystallization. It is possible that all channel regions of theswitching transistors of the unit pixels may be formed of the MILCpolycrystalline silicon film. The driving transistors of the R and Gunit pixels have an amorphous silicon film between the polycrystallinesilicon films and the driving transistor of the B unit pixel may have achannel region made of a polycrystalline silicon film.

[0069] In The present invention described above, achieves the whitebalance without increasing the pixel area but by changing currentmobilities or resistance values of the channel layers of the R, G and Bunit pixels.

[0070] Also, the present invention may reduce processing costs andsimplifying the process by crystallizing the amorphous silicon film intothe polycrystalline silicon film using the MIC/MILC crystallizationmethods and then forming semiconductor layers of the driving transistorsof the R, G and B unit pixels having different current mobilities.

[0071] Although the preferred embodiments of the present invention havebeen disclosed for illustrative purposes, those skilled in the artappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A flat panel display, comprising: a plurality ofpixels, each of the pixels including R, G and B unit pixels to embodyred (R), green (G) and blue (B) colors, respectively, and each of theunit pixels including at least one transistor, wherein transistors of atleast two unit pixels of the R, G, and B unit pixels include channellayers with different current mobilities.
 2. The flat panel displayaccording to claim 1, wherein each of the at least one transistor in theR, G and B unit pixels includes a channel layer having the same size ineach pixel.
 3. The flat panel display according to claim 1, wherein theR, G and B unit pixels each further include a light-emitting device, andtransistors to control currents supplied to the light-emitting devicesof each unit pixel include the channel layers having the same size ineach pixel.
 4. The flat panel display according to claim 1, wherein theR, G and B unit pixels further include a light-emitting device driven byat least one transistor, where current mobility of a transistor to drivea light-emitting device having the highest luminous efficiency among thelighting-emitting devices of the unit pixels is lower than the currentmobility of at least one transistors to drive lighting-emitting deviceshaving a relatively low luminous efficiency.
 5. The flat panel displayaccording to claim 1, wherein the channel layers of the transistors ofthe R, G and B unit pixels are made of polycrystalline silicon filmshaving different crystallization directions from one another.
 6. Theflat panel display according to claim 5, wherein the R, G and B unitpixels each further include a light-emitting devices driven by thetransistors, respectively, where a channel layer of a transistor todrive a light-emitting device having the highest luminous efficiencyamong the light-emitting devices is made of a metal inducedcrystallization (MIC) polycrystalline silicon film, and channel layersof transistors to drive light-emitting devices having relatively lowluminous efficiency are made of a metal induced lateral crystallization(MILC) polycrystalline silicon film.
 7. The flat panel display accordingto claim 1, wherein the R, G and B unit pixels each further include alight-emitting device driven by the transistors, respectively, and theR, G and B unit pixels each includes a driving transistor to drive thelight emitting device and a switching transistor to the drivingtransistor switch on or off.
 8. The flat panel display according toclaim 7, wherein the channel layers of the switching transistors of theR, G and B unit pixels are made of a MIC polycrystalline silicon film,and wherein a driving transistor of a unit pixel having the highestluminous efficiency among the R, G and B unit pixels has a channel layermade of the MIC polycrystalline silicon film and driving transistors ofunit pixels having a relatively lower luminous efficiency have channellayers made of a MILC polycrystalline silicon film.
 9. The flat paneldisplay according to claim 7, wherein the channel layers of theswitching transistors of the R, G and B unit pixels are made of a MILCpolycrystalline silicon film, and wherein a driving transistor of a unitpixel having the highest luminous efficiency among the R, G and B unitpixels has a channel layer made of a MIC polycrystalline silicon filmand driving transistors of unit pixels having a relatively lowerluminous efficiency have channel layers made of the MILC polycrystallinesilicon film.
 10. The flat panel display according to claim 7, wherein aswitching transistor and a driving transistor of a unit pixel having thehighest luminous efficiency among the R, G and B unit pixels havechannel layers made of a MIC polycrystalline silicon film, and drivingtransistors and switching transistors of unit pixels having a relativelylower luminous efficiency have channel layers made of a MILCpolycrystalline silicon film.
 11. In a flat panel display wherein thedisplay comprises a plurality of pixels, each of the pixels including R,G and B unit pixels, and each of the unit pixels includes at least onetransistor, a method for manufacturing the flat panel display comprises:forming an amorphous silicon film on an insulating substrate; forming afirst mask and a second mask for metal induced lateral crystallization(MILC) on the amorphous silicon film; depositing an metal film for MILCover the substrate; crystallizing the amorphous silicon film into apolycrystalline silicon film in order that a portion corresponding tothe first and second masks is crystallized by a MILC method and aremaining portion is crystallized by a metal induced crystallization(MIC) method; removing the first and second masks and the metal film;and patterning the polycrystalline silicon film in order that asemiconductor layer of a transistor of a unit pixel having the highestluminous efficiency among the R, G and B unit pixels is made of thepolycrystalline silicon film crystallized by the MIC method, andsemiconductor layers of transistors of unit pixels having a relativelylower luminous efficiency is made of the polycrystalline silicon filmcrystallized by the MILC method.
 12. A flat panel display, comprising aplurality of pixels, each of the pixels including R, G and B unit pixelsto embody red (R), green (G) and blue (B) colors, respectively, and eachof the unit pixels including a transistor, wherein the transistor of atleast one unit pixel among the R, G, B unit pixels includes a channelregion made of silicon layers having a different film quality.
 13. Theflat panel display according to claim 12, wherein the transistors of atleast two unit pixels among the R, G and B unit pixels include channelregions made of silicon layers of at least one different film quality,and wherein lengths of the silicon layers having low current mobilitiesof the channel regions are different.
 14. The flat panel displayaccording to claim 12, wherein the transistors of the R, G and B unitpixels include channel layers having a same length.
 15. The flat paneldisplay according to claim 12, wherein the R, G and B unit pixels eachfurther include a light-emitting device, respectively, and transistorsto control currents supplied to the light-emitting devices of the unitpixels include channel layers having a same length.
 16. The flat paneldisplay according to claim 15, wherein a channel region of a transistorcorresponding to a light-emitting device having the lowest luminousefficiency among the light-emitting devices of the R, G and B unitpixels does not include the silicon layer having low current mobility orincludes the silicon layer having low current mobility which has asmaller length than channel regions of transistors corresponding tolight-emitting devices having relatively higher luminous efficiency. 17.The flat panel display according to claim 14, wherein the channel regionis made of a polycrystalline silicon layer and an amorphous siliconlayer.
 18. The flat panel display according to claim 14, wherein thesilicon layer having the low current mobility in the channel region ismade of the amorphous silicon layer.
 19. In a flat panel display whichcomprises a plurality of pixels, each of the pixels including R, G and Bunit pixels to embody red (R), green (G) and blue (B) colors,respectively, each of the unit pixels including a transistor, a methodfor manufacturing the flat panel display comprising: forming anamorphous silicon film on an insulating substrate; forming a first maskto a third mask formetal induced lateral crystallization (MILC) on theamorphous silicon film; depositing a metal film for MILC over thesubstrate; crystallizing the amorphous silicon film into apolycrystalline silicon film in order that the amorphous silicon film ispartially remained only under the first to third masks; removing thefirst to third masks and the metal film; and patterning thepolycrystalline silicon film in order that the amorphous silicon filmexists between the polycrystalline silicon films to form semiconductorlayers of the transistors of the R, G and B unit pixels, wherein channelregions of the transistor of the R, G and B unit pixels have resistancevalues determined by lengths of the amorphous silicon films existingbetween the polycrystalline silicon films.